MODEL RELEASED. Nuclear magnetic resonance (NMR) spectroscopy. Scientist examines NMR spectrum of a protein on the computer screen of an NMR spectro- meter. The principles of NMR spectroscopy are based on the premise that the spin of certain chemical nuclei generate magnetic fields. When these magnetic nuclei are subjected to a uniform magnetic field their attempts to line up with the field result in a wobble (a precession) about the field direction. This precession frequency depends on the type of nucleus and strength of field. Nuclei are identified by measuring their precession frequencies at a known field strength.